LAUSR

Fluoride is a colourless micro-nutrient which is highly required for the strong teeth and bones. The above and below the prescribed range (0.6–1.5 mg/l) of fluoride in drinking water is harmful or hazardous for human health. Granite gneiss and pegmatite are the natural sources of fluoride minerals in this North Singbhum Craton. Purulia district which is the extended part of Chhota Nagpur Gneissic complex hosts such fluoride bearing rocks and minerals. About 619 water samples were collected from different parts of the district. Different rock samples have been collected from exposed litho-strata with prominent geological structures through Garmin GPS Etrex 30x. Sample sites have been geocoded on SRTM DEM and rocks are tested in the laboratory to examine the concentration of fluoride ions. The study was conducted to identify the natural and anthropogenic sources of fluoride and find out the relationship among the fluoride, geology with structures, hydro-geomorphology, soil and aquifer. Lineament features have been extracted using different bands of two specific images, namely ETM and ASTER. Digital mapping techniques including spatial analysis are used to detect the geomorphological attributes using SRTM and ASTER DEM data with adequate ground verification. Finally, Fluoride Contamination Index (FCI) map has been prepared by Thomas L. Saaty (1984) Analytical Hierarchy Process (AHP) using weighted sum method (WSM) in the range between 1 and 10 on the basis of their percentage of contamination. The study shows that high and very high fluoride content (3.52–5.50 mg/l and more than 5.50 mg/l) is found in the undulating plateau with dissected valley while granite gneiss and pegmatite are the dominant fluoride bearing rocks. Fluoride minerals are being released from structural weak zones through various mobile agents and ultimately mixed into the soils and groundwater. The high and very high contaminated zones (37.79%) reveal moderate to good groundwater yield pockets of unconfined and semi-confined aquifers and larger population of these regions are exposed to fluoride vulnerability.